The invention relates generally to carburetors for internal combustion engines, and more particularly to power valve devices for step-wise increasing the amount of fuel provided to the carburetor when manifold vacuum drops below a predetermined level.
Despite the ubiquitous use of fuel injection, carburetors remain in use in many internal combustion engines. Of particular interest are high performance carburetors used in racing engines and high-performance street engines. Professionals and amateurs alike strive to obtain the most useable power possible from engines used in vehicles for competitive and recreational purposes. Aftermarket carburetors and components, usually in combination with other engine parts, provide a ready means for substantially increasing the performance of a stock engine. Large after-market carburetor manufacturers such as Holley provide many products and much technical information to supply this market.
Basically, carburetors employ jets with calibrated holes to meter fuel from a float bowl that is filled with liquid fuel, such as gasoline or alcohol, to a Venturi tube throat wherein the fuel becomes mixed with air in the proper proportion for optimum combustion. The mixture of air and fuel is conducted through an intake manifold into the combustion chamber(s) of the engine. The amount of fuel delivered by the jets to the throat is dependent on the amount of air drawn through the throat by engine vacuum, which is controlled by opening or closing a throttle valve that is typically disposed at the juncture of the carburetor and the intake manifold.
A power valve is an additional valve in the carburetor that operates in parallel with the jets to conduct an additional quantity of fuel from the float bowl to the throat when manifold vacuum reaches a predetermined low level, i.e., when the throttle is opened a sufficient amount. The valve improves the engine""s responsiveness in making the transition from idle to full throttle and, therefore, improves acceleration.
The power valve is threadably received in a xe2x80x9cmetering blockxe2x80x9d that contains the jets and that is mounted to the carburetor so as to form one side of the float bowl. An exemplary prior art power valve and metering block are shown and described (particularly at pages 33-35 and 56-59) in the publication xe2x80x9cHolley Techxe2x80x9d by Alex and Nancy Walordy, of Westbury, N.Y. (ISBN #0-941167-04-6), herein incorporated by reference in its entirety.
One end of the power valve includes a fuel inlet for admitting fuel from the float bowl into the valve. The other end of the power valve houses a diaphragm that is in fluid communication with the engine""s intake manifold, the diaphragm being displaced by engine vacuum against a spring bias to hold the valve closed until the vacuum drops to a predetermined barometric pressure. When the manifold pressure drops to the predetermined level, the spring moves a plunger so as to unseat an inlet end of the plunger from an inlet seat of a tubular aperture through the valve for conducting fuel.
The metering block includes a frustoconical power valve receptacle. This receptacle typically has two holes therethrough that form ends of respective passageways in the metering block known in the art as a xe2x80x9cpower valve channel restrictions,xe2x80x9d leading to respective carburetor throats. There are typically four throats or barrels in high performance carburetors, and therefore two metering blocks.
The holes forming the ends of the power valve channel restrictions are typically not aligned along a diameter of the valve seat in high performance carburetors. Instead, they are typically biased toward the lower portions of the power valve receptacle to varying degrees, to prevent the tendency for the adjacent fuel level to uncover the holes and starve the engine when cornering or turning the vehicle.
The power valve is seated against an annular washer applied around the power valve receptacle that spaces an annular flange portion of the power valve above the power valve receptacle. Outlet holes or apertures extend from the interior passageway of the power valve through the annular flange portion of the power valve, forming a fuel outlet of the power valve. Fuel passing into the power valve at its inlet, through the interior passageway of the power valve, and out the outlet holes or apertures of the power valve moves through the annular space created between the annular flange portion of the power valve and the frustoconical power valve receptacle in the metering block and into the power valve channel restriction on its way to the carburetor throat.
In the earliest power valves, there were typically four or six circular holes, equally angularly spaced around the annular flange portion of the power valve. In modern power valves, the circular holes are typically replaced by two rectangular shaped apertures that are aligned along the diameter of the annular flange portion of the power valve, in an attempt to increase the flow rate through the valve, and to provide even flow to the power valve channel restrictions. The total area of the rectangular apertures is substantially larger than the area of the inlet of the power valve, in an attempt to maximize flow through the valve.
The metering block is a relatively closely toleranced and expensive part that is designed to meter the optimum amount of fuel required during maximum acceleration. The power valve, on the other hand, is a relatively inexpensive part that functions simply as an xe2x80x9con/offxe2x80x9d switch and is designed for ease of replacement. As the valve is threaded into the metering block, the alignment of the aforementioned holes or apertures forming the outlet of the valves align unpredictably with respect to the power valve channel restrictions. This is especially so in high performance carburetors where the holes of the power valve channel restriction in the power valve seat are biased off the diameter, toward the lower portion of the power valve seat. These holes are therefore displaced from one another more than 180 degrees. Accordingly, a 180 degree rotation of the power valve is required to move from one position of the power valve wherein optimum alignment is achieved, to the next. Therefore, even if the carburetor""s metering system is adjusted to perfectly accommodate the flow pattern provided by a particular prior art power valve, replacing that valve with another typically requires substantial readjustment.
The move to employing two diametrically opposed rectangular outlet apertures in the prior art power valve is believed to have resulted from a recognition of the importance, in high performance carburetors having multiple throats, of providing uniform flow to the power valve channel restrictions. However, the present inventor has recognized that there remains substantial imbalance in the fuel flow to the power valve channel restrictions remains which is detrimental to engine performance. This is because of the aforementioned unpredictability of alignment of the apertures when threading the power valve in to the metering block, especially in high performance carburetors.
The present inventor has recognized some additional problems with prior art power valves. As mentioned, the power valve is intended to function in combination with the metering system provided by the metering block as simply an on/off switch, with the metering block providing for metering of fuel. However, regardless of the amount of fuel the valves pass, a significant flow restriction or pressure drop is imposed in prior art power valves, and this detracts from the ability of the metering block to optimize flow. For example, the present inventor has found that there is a significant flow restriction at the inlet end of the plunger and the inlet seat of the tubular aperture.
Accordingly, there is a need for a high performance power valve for a carburetor that provides for reducing the flow restriction imposed by prior art power valves, and that may be used as a replacement part for an existing power valve in the carburetor.
The high performance power valve for a carburetor according to the present invention solves the aforementioned problems and meets the aforementioned need by providing, in one aspect, a housing having an annular flange portion through which extend more than two rectangular outlet apertures for conducting fuel received from a tubular aperture in the housing to one or more power valve channel restrictions. This achieves better alignment between the apertures and the power valve channel restrictions for balancing fuel flow to the power valve channel restrictions. Preferably, four such outlet apertures are provided at radially symmetrically spaced intervals about the annular flange portion.
In another aspect, preferably, an interior surface of the tubular aperture is radiused substantially where this surface meets the outlet apertures.
In yet another aspect, a high performance power valve for a carburetor according to the present invention provides a housing, a tubular aperture through the housing for conducting fuel, and a plunger disposed in the tubular aperture which contacts a seat thereof for shutting off fuel flow through the valve. The seat is preferably radiused a substantial amount compared to the thickness of the seat in the region where this contact is made for reducing flow restriction. The plunger is also preferably radiused a like amount in the region where this contact is made.
In still another aspect, a high performance power valve for a carburetor according to the present invention provides a housing having an annular flange portion through which extend one or more outlet apertures for conducting fuel, and a tubular aperture through the housing for conducting fuel to the outlet apertures, wherein the annular flange portion extends into the tubular aperture to form one or more xe2x80x9cvanesxe2x80x9d corresponding to the outlet apertures for reducing turbulence.
Therefore, it is a principal object of the present invention to provide a novel and improved high performance power valve for a carburetor.
It is another object of the present invention to provide a high performance power valve for a carburetor that provides for reducing the flow restriction imposed by prior art power valves.
It is yet another object of the present invention to provide such a high performance power valve for a carburetor adapted for employing a prior art power valve.
It is still another object of the present invention to provide such a high performance power valve that can be employed as a replacement part for the prior art power valve.
The foregoing and other objects, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings.